Traveling wave electron discharge devices



May 6, 1958 T. J. MARCHESE TRAVELING wAvE ELx-:cTRoN DISCHARGE DEVICES 2Sheets-Sheer. l

Filed Feb. 4, 1954 mm @n wm n mm vew G May 6, 1958 T. J. MARCHESETRAVELING wAvE ELEcTRoN DISCHARGE DEVICES 2 Sheets-Sheet .2

fla/0 007' Filed Feb. 4,v 1954 w n E w IIIIIIIL IWA' INVENTOR r//fOoO/QEd MARCHA-S6 BY K ATTO R N EY nite TRAVELHNG WAVE ELECTRN DlSCHARGE lDEVICES Application February 4, 1954, Serial No. 408,266

20 Claims. (Cl. S15- 3.5)

This invention relates to traveling Wave electron discharge devices andmore particularly to means for extracting radio frequency energytherefrom having practical application in high power traveling waveamplifier types.

Traveling wave amplifier tubes heretofore proposed have been ofrelatively low power and have been cooled by heat radiation from thecomponents of the electron discharge device. However, when the powerhandling capability of a traveling wave electron discharge device isincreased above say a kilowatt, it is necessary to provide a coolant todissipate the heat.

An object of this invention is to provide a traveling wave tube having astructural configuration capable of being adapted to provide passagesfor a fluid `coolant to increase the dissipation of heat from thetransmission line and coilector anode thereof.

Another object of this invention is to provide a furcated means at theoutput portion of the traveling wave electron discharge device capableof handling without interaction the three different energies present inthe electron beam, the radio frequency energy and the fluid coolant.

A further object of this invention is to provide a novel combination ofelements at the output portion of the traveling wave electron dischargedevice for matching the energy on a helical transmission line to aconventional coaxial type transmission line.

A feature of this invention is the provision of a furcated microwaveenergy junction having a transition section in a first branch thereofcoupled to the helical propagating structure and a shorting element in asecond branch thereof to cooperate with said first branch in transducingradio frequency energy from said propagating structure to a conventionalmicrowave transmission line through a third branch of said junction. Thefirst branch is adapted to pass the electron beam axially thereof to avwater-cooled collector anode, and the second branch includes a passagefor the circulation of a liuid coolant through said transmission line.

Another feature of this invention provides a furcated coaxialtransmission line junction including a transition section as the innerconductor of a first branch thereof, said transition section including acylinder having a helical slot longitudinally thereof whose pitch isgradually varied from an infinite pitch adjacent the junction of saidbranches to a pitch corresponding to the uniform pitch of a helicalpropagating structure. Cooperating with said first branch is included asecond branch having shorted inner and outer conductors to provide amatched transition of energy from the propagating structure to a thirdbranch of said junction for ultimate utilization of the energyexternally of the traveling wave device.

A further feature of this invention is the provision of a novel metal toceramic seal included in the third brauch of the furcated junctiondevice to provide a vacuum closurefor a traveling Wave electrondischarge device, said seal incorporating as an intimate portionvthereof arent lO atmospheric terminal means for extraction of energyfrom said device.

The above-mentioned and otherl features and objects of this inventionwill become more apparent by reference to the following descriptiontaken in conjunction with the accompanying drawings, in which:

Fig. l is a schematic illustration in longitudinal section of atraveling wave electron discharge device incorporating a furcatedmicrowave energy junction as the radio frequency energy output means inaccordance with the principles of this invention;

Fig. 2 is a longitudinal sectional view illustrating the details of theradio frequency output means of this invention;

Fig. 3 is an enlarged sectional View of the radio frequency extractingbranch of the furcated junction illustrating the metal to ceramic sealof this invention;

Figs. 4 and 5 are schematic sectional illustrations of other embodimentsof the furcated microwave energy junction of this invention; and

Fig. 6 is a bottom plan view of Fig. 5.

Referring to Fig. l, there is illustrated schematically a high powertraveling wave electron discharge device capable of amplifying radiofrequency energy having a power output in the order of 10 kilowatts. Thetraveling wave device is shown to comprise an envelope l enclosing theinternal structure thereof, consisting of a nonmagnetic material, suchas Monel. At one end of envelope i. is disposed an electron gun unit 2for projecting an electron beam along the axis of envelope 1 toward thecollector anode assembly 3 disposed at the opposite end of envelope l.intermediate electron gun unit 2 and collector assembly 3 is disposed aninteraction section i adjacent the axial path of the electron beam toprovide a means for propagating radio frequency energy therealong in aninteracting relation with the electrons of the beam. An input couplingmeans 5 disposed adjacent electron gun unit 2 provides a means forcoupling radio frequency energy into interaction region 4 whose primarypurpose is the amplification of the thusly injected radio frequency. Theamplied radio frequency energy is coupled from the interaction region 4for further utilization by means of output coupling means 6 disposedadjacent collector assembly 3.

The electron gun unit 2 may take any known configuration including thenecessary electrodes therein to provide an electron beam for travelaxially of envelope 1. in high power operation, the unit 2 shouldprovide an electron beam having high current density. A unit 2 capableof providing the required high current density would, for example, be ofthe rectilinear type; that is, the electrons leave the surface of thecathode normal thereto and travel in parallel paths along the axis ofenvelope l, said gun unit having a rating in the order of 6,000 voltsand 5 amps. To keep the beam collimated, the entire traveling Wavedevice is immersed in an axial magnetic field as provided by a solenoid7 or a permanent magnet structure replacing solenoid 7 as taught in thecopending application of I. H. Bryant, Serial No. 318,060, filed October31, 1952, or in the copending applicationof I. H. Bryant and H. W. Cole,Serial No. 321,342, filed November 19, 1952, now abandoned.

The radio frequency input transmission line ti, illustrated as being acoaxial type, forms a component ot' input coupling means 5 with theinner conductor 9 thereof being connected to transformer section lilextending from gun unit 2 to the interaction section 4. Transformer 10has the primary purpose of matching the impedance of transmission line 8to the helical transmission line l1 forming the primary component of theinteraction section 4. This impedance match between the input radioassassinfrequency line and the helical propagating structure isnecessary to provide a substantially retlectionless transfer of energyfrom a low impedance transmission line having an impedance in the orderof 50 ohms to a high impedance helical transmission line having animpedance in the order of 600 ohms.

Referring to the interaction section 4, there is illustarted thereintransmission line or propagating structure` A1 formed from a hollowtubing in a manner to provide a helical propagating structure supportedaxially of the envelope 1 by means of ceramic support members 12.Transformer section is adapted to have a passage therethrough asindicated at 13 to provide through section 10 and helix 11 a passage toenable the circulation of a fluid coolant for achievement of the desireddissipation of heat developed on propagating structure 11 byinterception of the electron beam and by the ohmic losses of the R.F.energy. In considering the support members 12, an ideal support shouldhold each turn of helix 11 rigid with respectto the helix axis and toall other turns, it should have minimum elect on the electromagneticwave traveling therealong and it should be mechanically strong towithstand shock and vibration. The preferred. material for the helixsupporting members 12 is, of course, ceramic. A circular yoke 14 incooperation with screws 15 disposed at each extremity of the interactionsection 4 is employed to hold three helix supports 12 on a 120 spacing.The ceramic supports 12 engage transformer section 10 at the electrongun unit end of the envelope 1 and engage transition section 16 at thecollector end of envelope 1 to establish the necessary axial alignmentthereof. If the yoke 14 is made of spring material, such a molybdenum,the assembly may be spring loaded.y An alternative to the positioning ofsupport members 12 is to increasethe radial thickness of the supportmembers to engage the envelope 1 wherein the envelope 1 is utilized tohold these three supports on e120" spacing.

As is the case in all traveling wave electrony discharge devices, acertain amount of energy propagating along structure 11 will berellected from the output coupling means back along propagatingstructure 11 causing an undesired oscillation to occur in theinteraction region of a traveling wave electron discharge device. It hasbeen recognized in the prior art that the application of a lossymaterial to a given portion of the interaction section will absorb thereiiected waves and thereby reduce the possibilities of undesiredoscillations. In the interaction region 4 of the traveling wave electrondis-- charge device herein disclosed, it is to be understoodv that thereis disposed a suitable attenuating material, such as aquadag, adjacentthe electron gun end of region 4Y in contact with the support members 12or the structure 11 itself to provide the desired absorption ofreflected wave energy.

The structural arrangement of electron gun unit 2, the collector anode3, the interaction section 4 and the input coupling means S withinenvelope 1 in a coactingv relationship has been established. Thepresence of three dierent energies within this structural` organizationpre-- sents a problem of matching the propagating structure 11 to anoutput transmission line Yfor undisturbed trans fer of amplified radiofrequency energy out of the traveling wave electron discharge device toa desired utilization means and at the same time provide means forpassage of the beam electrons to the anode of collector assembly 3 andthe circulation of a coolant for cooling the propagating structure 11.incorporated as means 6 satisfies the above requirements for handlingthe three energies independently,y and is;l

illustrated in Fig. 2 as a universal T-type junction section 17.

The drawing of Fig. 2 illustrates that outputcoupling means 6 includes.a furcatedmicrowave junctionsectionr The microwave junction section 17having a rst branch or arm 18 including therein transition section 16 tocooperate in matching the high impedance of the structure 11 to thenominal 50 ohm impedance normally associated with coaxial typetransmission lines. Transition section 16 is coaxial of envelope 1 andincludes a cylinder 19 having a helical slot 20 therein whose pitch isgradually varied from an infinite pitch adjacent the junction of thebranches of said junction section to the pitch of the uniform helixforming structure 11. The transition section 16 may be configured totransform wave energy from a helix to a coaxial type transmission linewith small values of reliection coetlicient over a wide frequency rangesuch as normally employed in traveling wave type electron dischargedevices. the fact that it behaves as a'transducer between a helicalstructure and a coaxial line with reasonable dimensions of the centerconductor and is mechanically rigid compared with the kind of transitionwhere the helix wire has the same dimension over the transition.Further, transition section 16 encloses the electron beam, introducinglittle if any, distortion into the electron optical system and allowsthe beam` to pass axially thereof to collector assembly 3 by means ofpassage 21. Energy traversing section 16 is transformed from its helicalmode of propagation to a TEM mode of propagation.

A second branch or arm 22 of junction section 17 includes an outerconductor 23 connected to envelope 1 which is maintained at a referencepotential, normally ground, and an inner conductor 24 is connected tocylinder 19- of transition section 16. The coaxial structure ofr'branch22 enables the coupling of transduced energy from section 16 propagatingin a TEM mode to an external coaxial transmission line (not shown) for`ultimate utilization of the derived interacted energy. Branch 22 furtherincludes as a component thereof a ceramic to metal seal 25 to assure. avacuum enclosed system for envelope 1 and to provide a support foratmospheric terminal means for connection of an external transmissionline thereto for utilization of the radio frequency energy passingthrough the device. As an embodiment of the structure described, thephysical size of structure 11 and section 16 required the use of a 3"external coaxial line for coupling to branch 22 of junction 17.

A third branch or arm 26 of section 17 cooperates with branch 18 andbranch 22 to assure a reflectionless transfer of radio frequency energyfrom structure 11 to the external coaxial transmission line. Thiscooperation is afforded by a diaphragm 27 disposed crosswise innerconductor 28 and outer conductor 29 in a manner to reflect apredetermined condition at the junction between cylinder 19 andconductor 24 of branch 22. Branch 26 further functions to provide apassage 30 in the form of a tube associated with inner conductor 28,continuing the `tluid passage established by the tubing of structure 11and the passage 31 disposed in transition section 16 for adequatecirculation of fluid coolant to remove heat from these structures.Passage 30 is extended through diaphragm 27 to end cap 32 and, hence,through nipple 33 to an external circulation arrangement (not shown).

The. junction 17 when conventionally employed in broadband applicationsis used as a junction and as a bend. The application of the T-typefurcated microwave junction in combination with a traveling wave tubefunctions as a bend to match the output transmission line (not. shown)to the helical propagating structure 11 to Having completed itsinteraction with the wave energy on propagating structure 11, theelectron beampasses Other advantages of such a transition is 1 rationwhere the ybranches extending from the axisof the envelope areperpendicular thereto and 180I with respect to each other. :Severalvrepresentative alternative contigurations arefillustrated inV Figs. 4,and 6 wherein the branches 22 Land 26 are at angles relative to the axisand to Veachother, other than 90 and 180, respectively. Components shownin Figs. 2 and 3 are identied' in Figsy4, 5 and 6 by 'the samel numberhaving a suix a or b attached thereto.

Fig. 4 illustrates schematically the identical structure shown anddescribed in Figs. 2 and 3, but where the branches 22a and 26a are otherthan perpendicular to the axis of envelope la while still displaced 180with respect to'each other. The illustration shows that each branch isat the same angle with respect to the axis of envelope 1, but it iswithin the-scope of this invention todisplace each of the branches at adifferent' angle relative to the axis independentof each other.

Figs. 5 and 6Y illustrate schematically the same structure of Figs. 2and 3, but where branches 22h are other than perpendicular to the axisof envelope 1b and branches 22h and 2Gb are displaced at 90 relative toeach other. A certain specific angular displacement between each branchand the branches and the axis is illustrated in the present showing, butit is well within the scope ofV this invention to dispose the branchesat any required angle relative'to each other and to the axis of envelope1 to conform to the application of the device incorporating the outputmeans 6 herein described.

While the transducing or output coupling means of this invention hasvbeenA described herein withv particular reference to a high powertraveling wave electron discharge device thereby necessitating-a fluidcooling system, it will be obvious to those skilled in the artthat saidoutput means may be utilized in low power traveling wave electrondischarge devices without departing from the spirit of this invention.It is to be clearly understood therefore, that this description is madeonly by `way of example and not as a limitation to the scope of myinvention as setforthin theA objects thereof and inthe accompanyingclaims.

I claim:

l. A traveling wave electron discharge-device comprising a vacuumenvelope having conductive cylindrical portions, an electron gun unitdisposed at one end of said envelope to project an electron beam alongan axial path within said envelope, a collector at the other end of saidenvelope to collect the electrons of said beam, a Wave propagatingstructure includinga helical transmission line of hollow tubingproviding therein a passage for a liquid coolant disposed'adjacent saidpath for transmission of radio frequency energy in interacting relationwith the electrons of said beam, input coupling means disposed adjacentsaid gun unit to couple radio frequency energy to said propagatingstructure, and an output coupling unit disposed adjacent said collectorto remove radio frequency energy from said propagating structure, saidoutput coupling unit including a furcated transmission line junctionsection having rst, second and third branches, said first branch beingdisposed coaxially of said conductive cylindrical portion and coupled tosaid propagating structure, said first branch also having a passagetherealong for coolant from said propagating structure in non-interioring relation with the iield of said radio frequency energy, said secondbranch serving as an output for radio frequency energy, and said thirdbranch having a tiuid connection for the coolant passage of said iirstbranch in non-interfering relation with the tield of said radiofrequency energy andmeans within said third branch and inconpledrelation to the conductive portion of said envelope to provide animpedance matching stub for the junction betweenasaid second branch andsaid propagating stnlcture.

'-2. .JA `deviceSfaccording =to -claim 1,- wherein :said first branchincludes' aftransition section coextensive with" said fil transmissionlinehavingsaid passage therethrough for the` circulation of the helicaltransmission line coolant and said second branch includes an outerconductor coupled to said envelope and an inner conductor coaxial ofsaid outer conductorcoupled to said transition section.

3. A device according to claim 2, wherein said transition sectionincludes a hollow cylinder coaxial of said path having a helical slotlongitudinally thereof whose pitch is gradually varied `from an innitepitch adjacent the junction of said branches to a pitchcorresponding tothe uniform pitch of said helical transmission line.

4. A device according to claim 3, wherein said inner conductor isconnected to said hollow cylinder at a given point in the iniinite pitchportion of said helical slot.

5. A device according to claim l, wherein said tirst branch includes atransition section coextensive with said transmission line having saidpassage therethrough for the circulation of the helical transmissionline coolant and said third branchincludes an outer conductor coupledto' said envelope, an inner conductor coaxial of said outer conductorcarrying therewith a passage for said iluid coolant, and an end capclosing said outer conductor to provide a vacuum closure for said thirdbranch including a nipple extending therethrough for external access tothe passage for said uid coolant.

6. A device according to claim 5, wherein said third branch furtherincludes a diaphragm structure extending radially from said innerconductor to said outer conductor to provide a shorting elementcrosswise of said third branch.

7. A device according to claim l, wherein said third branch includes anouter conductor coupled to the conductive portion of said envelope, aninner conductor coaxial of said outer conductor having therein a passagefor said helical transmission line uid coolant, an end cap closing saidouter conductor to provide a vacuum closure for said third branchincluding an aperture therein for external access to the passage forsaid fluid coolant, and means extending radially from said innerconductor to said outer conductor to provide a shorting elementcrosswise said third branch.

8. A device according to claim l, wherein said second branch includes anouter conductor coupled to the conductive portion of said envelope, aninner conductor coaxial of said outer conductor coupled to saidtransmission line, and a ceramic to metal seal disposed to extend be-.tween saidinner and outer conductors to provide a vacuum seal for saidsecond branch, said seal including terminal means for extraction ofenergy from said device.

9. A device according to claim 8, wherein said seal includes a ceramicdisk having an axial aperture therein, said outer conductor having anoutwardly extending shouldered portion to engage the top and peripheralportions of said disk, said inner conductor including-a hollowcylindrical portion having an inwardly extending shouldered portion toengage the top of said disk and the edge of said axial aperture, anouter conducting cylinder engaging the bottom of said disk including ahanged portion having an upwardly extending lip to hold said outwardlyextending shouldered portion against the periphery of said disk, anannular member having a downwardlyV extending lip to compress saidoutwardly extending shouldered portion against the top of said disk,means to secure said annular member to the ilanged portion of said outercylinder for application of a compressive stress tol said outwardlyextending shouldered portion, an inner conducting cylinder having ashank portion disposed in the axial aperture of said disk with ashouldered portion against the bottom of said disk, and means to apply acompressive stress to said inwardly extending shouldered portion, saidouter and inner cylinders providing a coaxial output terminal. Y

10.l A traveling wave electron discharge device` comprising a metallicvacuum envelope, an electron gun/unit disposed atone-I end ofsaidenvelope to project-an eleccent said collector to remove radio frequencyenergy from said propagating structure, said output coupling unitincluding a transmission line junction section having first, second andthird branches, said first branch being disposed coaxially of saidenvelope and coupled to said propagating structure, said first branchalso having a passage therethrough for liuid coolant from saidpropagating structure in non-interfering relation with the eld of saidradio frequency energy, said second branch serving as an outputconnection for radio frequency energy, and said third branch having apassage therein in noninterfering relation with the field of said radiofrequency energy coupled to the passage in said first branch forcirculation of said uid coolant, and a shorting element in said thirdbranch to effect an impedance match between said second branch and saidpropagating structure.

1l. In traveling wave electron discharge devices having an electron gununit to project an electron beam along a given path and a wavepropagating structure including a helical transmission line of hollowtubing providing therein a passage for a fluid coolant disposed adjacentsaid given path for transmission of radio frequency energy ininteracting relation with the electrons of said beam, an output couplingunit to remove radio frequency energy from said propagating structureincluding a furcated transmission line junction having first, second andthird branches, said first branch being disposed coaxially of said givenpath and electrically coupled to said transmission line, said firstbranch also having a passage therethrough coupled to the passage in saidline in non-interfering relation with the field of said radio frequencyenergy, said second branch serving as an output coupling for radiofrequency energy from said transmission line, and said third branchhaving a passage therein in non-interfering relation with the field ofsaid radio frequency energy coupled to the passage in said first branchfor circulation of said iiuid coolant, and means disposed crosswise saidthird branch to provide an impedance matching stub for the junctionbetween said second branch and said propagating structure.

l2. In a device according to claim ll, wherein said first branchincludes a transition section comprising a cylinder coaxial of said pathhaving a helical slot longitudinally thereof whose pitch is graduallyvaried from an infinite pitch adjacent the junction of said branches toa pitch corresponding to the uniform pitch of said helical transmissionline.

13. In a device according to claim 1l, wherein said second branchincludes an outer conductor coupled to a reference potential, an innerconductor coaxial of said first conductor coupled to said transmissionline, and a ceramic-to-metal seal disposed to extend between said innerand outer conductors to provide a vacuum seal for said second branch.

14. ln a device according to claim 13, wherein said seal includes aceramic disk having an axial aperture therein, said outer conductorhaving an outwardly extending shouldered portion to engage the top andperipheral portions of said disk, said inner conductor including ahollow cylindrical portion having an inwardly extending shoulderedportion to engage the top of said disk and the edge of said axialaperture, an outer conducting cylinder engaging the bottom of said diskincluding a anged portion having an upwardly extending lip to hold saidoutwardly extending shouldered portion against the periphery of saiddisk, an annular mem-ber having a downwardly extending lip to compresssaid outwardly extending shouldered portion against the top of saiddisk, means to secure said annular member tothe flanged portion of saidouter cylinder for application of a compressive stress to said outwardlyextending shouldered portion, an inner conducting cylinder having ashank portion disposed in the axial aperture of said disk with ashouldered portion against the bottom of said disk, and means to apply acompressive stress to said inwardly extending shouldered portion.

l5. In a device according to claim 11, wherein said third branchincludes a first conductor coupled to a reference point, a secondconductor coaxial of said first conductor having therein a passage forsaid fluid coolant, an end cap to close said first conductor to providea vacuum closure for said third branch including an aperture therein forexternal access to the passage for said iiuid coolant, and a diaphragmextending between said second conductor and said first conductor toprovide said impedance matching element.

16. A traveling wave electron discharge device comprising a vacuumenvelope having conductive portions, an electron gun unit disposed atone end of said envelope to project an electron beam along an axial pathwithin said envelope, a collector at the other end of said envelope tocollect the 'electrons of said beam, a wave propagating structuredisposed adjacent said path for transmission of radio frequency energyin interacting relation with the electrons of said beam, input couplingmeans disposed adjacent said gun unit to couple radio frequency energyto said propagating structure, and an output coupling unit disposedadjacent said collector to remove radio frequency energy from ysaidpropagating structure, `said output coupling unit including a furcatedtransmission line junction having first, second and third branches, saidfirst branch being disposed coaxially of a conductive portion of saidenvelope and coupled to said propagating structure to provide inconjunction with said envelope portion a coaxial waveguide, said secondbranch serving as a coaxial waveguide output terminal for radiofrequency energy, and said third branch having a shorting elementcoupled to said envelope portion to provide an impedance matching stubfor the junction between said second branch and said propagatingstructure.

17. A device according to claim 16, wherein said first branch includes atransition section coextensive with said propagating structure, saidtransition section including a cylinder coaxial of said path having ahelical slot longitudinally thereof whose pitch is gradually varied froman infinite pitch adjacent the junction of said branches to apredetermined pitch.

18. A device according to claim 16, wherein said second branch includesan outer conductor coupled to said envelope, an inner conductor coaxialof said outer conductor coupled to said propagating structure, and aceramic to metal seal disposed to extend between said inner and outerconductors to provide a vacuum seal for said second branch.

l9. A device according to claim 18, wherein said seal includes a ceramicdisk having an axial aperture therein, said outer conductor having anoutwardly extending shouldered portion to engage the top and peripheralportions of said disk, said inner conductor including a hollowcylindrical portion having an inwardly extending shouldered portion toengage the top of said disk and the edge of said axial aperture, anouter conducting cylinder engaging the bottom of said disk including aflanged portion having an upwardly extending lip to hold said outwardlyextending shouldered portion against the periphery of said disk, anannular member having a downwardly extending lip to compress saidoutwardly extending shouldered portion against the top of said disk,means to secure said annular member to the flanged portion of said outercylinder for application of a compressive stress to said outwardlyextending shouldered portion, an inner conduetingfcylinder, having a;shank portion. disposed. in; 111e.y References Cited in the le of thispatent axial. aperture of. said diskwith a shoulder portionagainstUNITED STATES PATENTS therbottom of `said dlsk, and means to apply acom-A -v outputtgrminaL 2,646,948 Pierce Apr. 28? 1953 2,637,775 LundMay 5,y 1953 20. A device according to claim 16, wherein said third andclosure means comprising a conductive short cross- 10 wise saidl thirdbranch.

